Recently, disease outbreaks have caused mass mortality among cultured penaeid shrimps in Asian countries. Since 1992, outbreaks of a new disease leading to serious mortality among populations of cultured kuruma shrimp (Penaeus japonicus) have occurred in northern Taiwan. The disease is characterized by obvious white spots on the carapace, appendages and the inside surface of the body, and cumulative mortality reaches 100% within 2-7 days. The diseased shrimps also display signs of lethargy and reddish coloration of the hepatopancreas. In 1993, white spot syndrome (W.S.S.) in cultured giant tiger prawn (P. monodon) and redtail prawn (P. penicillatus) was observed. Serious damage to penaeid shrimp production by W.S.S. in Taiwan has been reported (Tung et al. personal communication).
An epizootiological survey of kuruma shrimp in Japan reports similar findings (Nakano et al., Fish Pathology, 29 (2):135-139, 1994). According to the evidence from electron microscopy and the results of challenge tests with the filtrate from diseased shrimp lymphoid organs, the causative agent was a virus that was temporarily designated RV-PJ, a rod-shaped nuclear virus of Penaeus japonicus (Inouye et al., Fish Pathology, 29 (2):149-158, 1994; Takahashi et al., Fish Pathology, 29 (2):121-125, 1994).
To date, the prevalence of baculoviruses in cultured penaeid shrimps has been well documented (Lightner et al., Aquaculture, 32: 209-233, 1983). Among these penaeid baculoviruses, monodon baculovirus (MBV), baculoviral mid-gut necrosis virus (BMNV) and Baculovirus penaei (BP) were considered to be the most important because they have on occasions caused serious losses in infected shrimp populations (Couch, Nature 247 (5438): 22-231, 1974; J. Invertebr. Pathol., 24:311-331, 1974; Lightner & Redman, J. Invertebr. Pathology, 38: 299-302, 1981; Lightner et al. (1983), supra; Lightner et al., 1987; Sano et al., Fish Pathology, 15: 185-191, 1981).
Baculovirus-like viral particles were observed in the spontaneously diseased penaeid shrimp with W.S.S. (Tung et al., personal communication). This virus may possibly be the main causative agent for the W.S.S. that has occurred in Taiwan in penaeid shrimps. To prevent the spread of W.S.S. in shrimps, thereby rescuing the financial losses caused by this viral disease, it is necessary to identify the actual causative agent and then to develop a diagnostic method that is easy, accurate and not time-consuming in the detection of W.S.S. without sacrificing the whole subjects tested.